1. Field of the Invention
This invention relates in general to energy absorption devices and, in particular, to an adjustable energy absorption device used to dissipate the motion energy of a body in motion. More specifically, but without restriction to the particular embodiment hereinafter described in accordance with the best mode of practice, this invention relates to a series of groups of holes in a shock tube that adjustably engage an internal spiral groove to vary the orifice area in an energy absorption device.
2. Discussion of the Related Art
Numerous mechanical systems require energy absorption devices for dissipating the motion energy of a component element in the system. Such mechanical systems include, for example, pallet stops, rolling doors and refrigeration cases, piston control in air cylinders, medical equipment including CAT scanners, manufacturing transfer and conveyor lines, and industrial robotic equipment. The typical energy absorption device includes a sealed outer cylinder, an internal shock tube, a piston having a head portion and a rod portion for engaging the moving system component, and an accumulator for collecting fluid from the interior of the shock tube when the piston head moves into the tube. The absorption device is also provided with an orifice area that allows passage of fluid from the shock tube to the accumulator as the means for dissipating the energy received by the piston rod. A system of check valves and return passageways is also commonly provided to allow repeated circulation of fluid between the shock tube and the accumulator. After each cycle, the piston head is returned to the beginning of its stroke by a compression coil positioned within the shock tube.
Manufacturers of these energy absorption devices have found it desirable to make the devices adjustable so that they may be readily employed in a variety of mechanical systems. The adjustable feature of the device allows it to effectively dissipate a wide range of energies as directed into the device through the piston rod. In this manner, end users of the devices are given the option of adjusting the device to meet their particular system needs. These types of devices are commonly adjustable to accommodate a shock force of up to 1,000 pounds with a dissipation rating of as high as 650 inch-pounds per cycle.
Providing adjustability to the device has focused on varying the orifice area between the shock tube and the outer cylinder. It is commonly known that the dissipation of larger energies requires a greater orifice area. This absorption capacity is a function of accumulator and fluid volume as well as overall structural integrity of the device. Prior hereto, there has been proposed a number of ways to adjustably vary the orifice area in an energy absorption device of the type described above. One of these prior solutions, for example, includes forming a longitudinal broached slot along the interior surface of the outer cylinder. This broached slot serves as a channel for directing fluid from the shock tube into the accumulator. Fluid is directed into the slot through apertures formed in the shock tube. The orifice area of the apertures is made adjustable by use of spring biased metering pin positioned between the cylinder and the tube. A rotatable bevelled cam is situated at the free end of the pin to longitudinally move the pin across the apertures to thereby adjust the orifice area. Another previously proposed solution for providing adjustability to the orifice area includes using the broached slot in combination with modified shock tube apertures. The apertures are each provided with a tapered channel formed on an arc length segment passing over the aperture around the exterior surface of the shock tube. The tapered channels are thus perpendicularly situated relative to the broached channel. In this manner, when the shock tube is rotated within the cylinder, the distanced between the respective bottoms of the tapered aperture channels and the broached channel is changed thereby varying the orifice area. These prior approaches involve complicated machining operations to form the various required slots and channels, and may additionally include several mechanical parts which are subject to malfunction. Furthermore, fabricating and assembling these numerous mechanical components or scheduling the complicated and time consuming machining operations adds significantly to the cost of producing this type of device.
The hydraulic shock absorber illustrated in U.S. Pat. No. 4,044,865 to Tourunen includes an internal thread and a hole associated with each turn of the internal thread. As the cylinder wall is rotated relative to the sleeve, the orifice area may be adjusted. This type of device, however, requires a number of complicated machined parts for proper operation. In addition thereto, the adjustability of the device is not fine in that relatively small rotations cause substantial changes in the damping characteristics.